The present invention relates to a method of noncontacting monitoring the elastic properties of a material in either a solid or liquid state and more particularly to that of a metal or ceramic material as disclosed in allowed U.S. patent application Ser. No. 478,375, herein incorporated by reference. The invention as disclosed is directed to a method using noncontacting laser ultrasonic monitoring at the surface to determine the density or elastic qualities of a material.
Consolidating ceramic components from powder compacts requires sintering at high temperatures during processing. Often, their mechanical properties are controlled by the residual porosity in the host material. Improvements in efficiency of production and in the properties of ceramics could be achieved if the porosity could be monitored during the processing stage. Feedback of this knowledge would allow the sintering process to be optimized and the porosity of the material to be controlled.
Several types of optical laser-base ultrasonic detectors have been developed for noncontacting measurement of surface motion due to ultrasonic waves. In some cases these devices have been employed at high temperatures to record material properties during heating. However, the majority of these systems depend on phase sensitive detection of the light and require polished surfaces and strict alignment for adequate signal-to-noise ratio, and thus are not suitable for processes, such as, sintering, and plasma and electron beam hearth melting.
Due to its noncontacting nature, laser-ultrasonic techniques now open the possibility for real-time monitoring of materials in very hostile environments, as is encountered during processing. Prior to this work, ultrasonic wave measurements of the sintering of ceramics used buffer rods which made direct contact with the material. Only optical access to the sample being sintered is required with the laser-ultrasonic method as described.